1. Field of the Invention
The present invention relates to a gas turbine and a combined cycle plant comprising combined cycles of this gas turbine and a steam turbine.
2. Description of the Prior Art
As one conventional example of the mentioned art, that disclosed by the Japanese laid-open patent application Hei 9(1997)-4411 is known. A conventional gas turbine mentioned therein is what is called a double casing type gas turbine comprising an outer casing (outer structural shell as a container) and a blade ring (inner shell) constituting an inner casing. In this gas turbine, the blade ring is provided surrounding first stage and second stage portions and is fitted with a ring segment (shroud) surrounding each of turbine rotor blades constituting a cascade of first stage rotor blades and another ring segment (shroud) surrounding each of turbine rotor blades constituting a cascade of second stage rotor blades. Likewise, the blade ring is fitted with an outer shroud of each of turbine stator blades constituting a cascade of first stage stator blades and another outer shroud of each of turbine stator blades constituting a cascade of second stage stator blades.
Also, the blade ring is supported to the outer casing via a plurality of pins extending in a radial direction of a turbine shaft so as to be expandable and contractible in the radial direction of the turbine shaft. In the blade ring, there are provided two flow passages (plenums) so as to extend along the first stage and second stage rotor blade cascades, so that heating medium supplied from a heating medium supply source which is irrespective of the gas turbine operation is flown therethrough. Accordingly, in this gas turbine, heating medium of an appropriate temperature is supplied to the respective flow passages of the blade ring so that the respective blade rings (as well as the ring segments) may be expanded and contracted in the radial direction of the turbine shaft. As the result of this, even if the turbine rotor blade is thermally expanded or contracted in the radial direction due to temperature changes of the working fluid in operation, a gap between a blade tip of the turbine rotor blade and the ring segment can be adjusted appropriately and a loss at the rotor blade tip can be reduced.
However, if temperature of the working fluid changes in operation of the gas turbine, there occurs a thermal expansion and contraction also in an extending direction of the turbine shaft (axial direction) in the ring segment which is located around the turbine rotor blades for forming an annular flow passage and in the outer shroud of the turbine stator blade. For this reason, while the ring segment and the outer shroud of the turbine stator blade, which are adjacent to each other, are arranged to abut on, or engage with, each other so as to be expandable and contractible in the axial direction, respectively, a gap between these members is enlarged according to the degree of the thermal expansion or contraction of each of the members so that the working fluid may leak out therethrough to invite an increase of the loss.
In view of the problem in the prior art, therefore, it is an object of the present invention to provide a gas turbine which is able to reduce a loss at a rotor blade tip and to reduce a loss caused by leakage of working fluid through a gap between members constituting an annular flow passage as well as to provide a combined cycle plant comprising such gas turbine.
A gas turbine, as claimed in Claim 1 of the present invention, for generating power by expanding a high temperature high pressure working fluid at a plurality of stages of a turbine stator blade a cascade provided in a turbine casing and a plurality of stages of a turbine rotor blade cascade fitted to a turbine shaft, is characterized in comprising; a first blade ring, supported to the turbine casing so as to be expandable and contractible in a radial direction of the turbine shaft, corresponding to a first turbine stator blade cascade and a first turbine rotor blade cascade which constitute any one stage of the plurality of stages; a second blade ring, supported to the turbine casing so as to be expandable and contractible in the radial direction of the turbine shaft, corresponding to a second turbine stator blade cascade and a second turbine rotor blade cascade which constitute another stage adjacent to the one stage; a first heating medium flow passage, provided in the first blade ring, for circulating therethrough a predetermined heating medium; a second heating medium flow passage, provided in the second blade ring, for circulating therethrough the predetermined heating medium; and a communication member for connecting the first blade ring and the second blade ring to each other and for communicating the first heating medium flow passage and the second heating medium flow passage with each other.
In the turbine included in the above gas turbine, the first blade ring which corresponds to any one stage (the first stage, for example) and the second blade ring which corresponds to another stage adjacent to the mentioned one stage (the second stage, for example) are provided and members constituting the annular flow passage (outer shrouds of the stator blades, ring segments, etc.) are supported by these first and second blade rings. Also, the first blade ring has the first heating medium flow passage formed preferably so as to surround the outer circumferential periphery of the first rotor blade cascade and the second blade ring has the second heating medium flow passage formed preferably so as to surround the outer circumferential periphery of the second rotor blade cascade, and a heating medium, such as steam supplied from a predetermined heating medium supply source, is circulated through the first and second heating medium flow passages. Thereby, in operation of the gas turbine, even if the turbine rotor blade expands or contracts in the radial direction of the turbine shaft due to temperature changes of the working fluid, the first and second blade rings are expanded or contracted in the radial direction and the gap between the blade tip of the turbine rotor blade and the members constituting the annular flow passage can be adjusted appropriately.
In this gas turbine, in addition to the above, the first blade ring and the second blade ring are connected to each other by the communication member so that both of the blade rings are integrated substantially. Moreover, the first heating medium flow passage and the second heating medium flow passage are communicated with each other via a flow passage provided in the communication member. Accordingly, the heating medium supplied into the first heating medium flow passage, etc. is to flow through the flow passage of the communication member which connects the first blade ring and the second blade ring to each other and hence, like the first blade ring and the second blade ring, the communication member also expands and contracts corresponding to the temperature of the heating medium.
As the result of this, in the present gas turbine, the heating medium of an appropriate temperature is supplied into the first heating medium flow passage, etc. and thereby the communication member connecting the first blade ring and the second blade ring to each other is expanded or contracted and the position of the first blade ring and the second blade ring can be changed so as to correspond to and follow the constituting members of the annular flow passage which is expanded or contracted by the temperature changes of the working fluid, etc. By so doing, in the present gas turbine, the blade tip loss of the rotor blade can be reduced and the loss caused by leakage of the working fluid through the gap between the members constituting the annular flow passage can be reduced.
In this case, the mentioned gas turbine preferably further comprises a first annular member surrounding the first turbine rotor blade cascade and a second annular member surrounding the second turbine rotor blade cascade and is constructed such that a first outer shroud of each of turbine stator blades, which constitute the first turbine stator blade cascade, and the first annular member engage slidably with each other and the first outer shroud and the first annular member, respectively, are fixed at one side of their both sides in a flow direction of the working fluid to the first blade ring, and a second outer shroud of each of turbine stator blades, which constitute the second turbine stator blade cascade, and the second annular member engage slidably with each other and the second outer shroud and the second annular member, respectively, are fixed at one side of their both sides in the flow direction of the working fluid to the second blade ring.
Also, it is preferable that a seal member is interposed between the first outer shroud of each of the turbine stator blades, which constitute the first turbine stator blade cascade, and the first annular member and between the second outer shroud of each of the turbine stator blades, which constitute the second turbine stator blade cascade, and the second annular member, respectively.
By such arrangement, the loss caused by leakage of the working fluid through the gap between the ring segment and the outer shroud of the turbine stator blade, both of which constitute the annular flow passage, can be reduced effectively.
In this case, it is preferable that the seal member is formed in a wave-like cross sectional shape having a plurality of mountain-like winding portions and is arranged with the winding portions being directed to the radial direction of the turbine shaft.
In the mentioned construction, the size of the seal member is made so as to meet a planned maximum value of the gap between the ring segment and the outer shroud of the turbine stator blade. Thereby, even if the gap between the ring segment and the outer shroud of the turbine stator blade expands or contracts thermally, the seal member can be deformed elastically so that expansion or contraction of the ring segment and the outer shroud of the turbine stator blade may be absorbed smoothly and precisely. As the result of this, the gap between the ring segment and the outer shroud of the turbine stator blade can be sealed excellently. As the seal member, what is called an E seal, which is formed in the wave-like cross sectional shape by bending a metal member in a W letter shape, may be employed.
Also, it is preferable that the second blade ring is located downstream of the first blade ring in the flow direction of the working fluid and the heating medium which has passed through the second heating medium flow passage provided in the second blade ring is led into the first heating medium flow passage provided in the first blade ring via the communication member and this heating medium which has passed through the first heating medium flow passage is led into a transition piece interior of a combustor which burns the working fluid.
By employing such construction, the heating medium which has passed through the second blade ring (the second heating medium flow passage), the communication member and the first blade ring (the first heating medium flow passage), sequentially, can be further made use of for cooling the interior of the combustor transition piece. In this case, the heating medium is taken out easily from the combustor transition piece and the circulation system of the heating medium can be made simplified.
A combined cycle plant, as claimed in Claim 6 of the present invention, comprising a steam turbine cycle for recovering and reusing exhaust heat of a gas turbine, is characterized in that the gas turbine comprises; a plurality of stages of a turbine stator blade cascade provided in a turbine casing; a plurality of stages of a turbine rotor blade cascade fitted to a turbine shaft; a first blade ring, supported to the turbine casing so as to be expandable and contractible in a radial direction of the turbine shaft, surrounding the turbine rotor blade cascade of any one stage of the plurality of stages; a second blade ring, supported to the turbine casing so as to be expandable and contractible in the radial direction of the turbine shaft, surrounding the turbine rotor blade cascade of another stage adjacent to the one stage; a first heating medium flow passage, provided in the first blade ring, for circulating therethrough steam supplied from the steam turbine cycle; a second heating medium flow passage, provided in the second blade ring, for circulating therethrough the steam supplied from the steam turbine cycle; and a communication member for connecting the first blade ring and the second blade ring to each other and for communicating the first heating medium flow passage and the second heating medium flow passage with each other.
In the gas turbine constituting the mentioned combined cycle plant, the steam taken from the steam turbine cycle (bottoming cycle) is supplied into the first heating medium flow passage, etc. and thereby the communication member connecting the first blade ring and the second blade ring to each other is expanded or contracted and the position of the first blade ring and the second blade ring can be adjusted so as to correspond to and follow the constituting members of the annular flow passage which expand or contract due to the temperature changes of the working fluid, etc. By so doing, while the steam of the steam turbine cycle is made use of effectively, the blade tip loss of the gas turbine rotor blade can be reduced and the loss caused by leakage of the working fluid through the gap between the members which constitute the annular flow passage can be reduced as well .